Catheterization is used in diagnostic and therapeutic procedures. For example, a cardiac catheter is used for mapping and ablation in the heart to treat a variety of cardiac ailments, including cardiac arrhythmias, such as atrial flutter and atrial fibrillation which persist as common and dangerous medical ailments, especially in the aging population. Diagnosis and treatment of cardiac arrhythmias include mapping the electrical properties of heart tissue, especially the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy. Such ablation can cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. Various energy delivery modalities have been disclosed for forming lesions, and include use of microwave, laser and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall. In a two-step procedure—mapping followed by ablation—electrical activity at points within the heart is typically sensed and measured by advancing a catheter containing one or more electrical sensors (or electrodes) into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the endocardial target areas at which ablation is to be performed.
Another catheterization procedure is renal denervation (RDN). It is a minimally invasive, endovascular catheter based procedure using radiofrequency ablation aimed at treating hypertension. The sympathetic system fuels the release of certain hormones that affect and control blood pressure. In hypertension, the continued release of low-dose amounts of these hormones can increase blood pressure. Hypertension can be controlled by diet, exercise and drugs. However, resistant hypertension (commonly defined as blood pressure that remains above goal in spite of concurrent use of three antihypertensive agents of different classes) requires more aggressive treatments, including surgery. Resistant hypertension is a common clinical problem faced by both primary care clinicians and specialists. As older age and obesity are two of the strongest risk factors for uncontrolled hypertension, the incidence of resistant hypertension will likely increase as the population becomes more elderly and heavier.
It has been established that severing the renal nerves improves blood pressure. However, this procedure involves surgery and all its attendant risks, and often resulted in global sympathetic denervation below the chest. Being able to de-nervate, or silence, only the renal nerves through a catheter-based system is a crucial development. A small catheter is placed in the femoral artery and access to the nerves is gained through the renal artery. The nerves are embedded in the casings or layers around the renal arteries. By passing an energy source into the renal artery and transmitting a low-dose energy, radiofrequency ablation, through the catheter, inbound and exiting renal sympathetic nerves are impaired or “denerved” at selected locations along their lengths. This causes reduction of renal sympathetic afferent and efferent activity and blood pressure can be decreased.
In both cardiac ablation and renal ablation, ablation along a closed inner circumference or a narrow band in a vessel or tubular region can lead to stenosis, including narrowing, tightening or stiffening of the vessel or tubular region. Accordingly, catheters with different 3-D designs have been employed to form conduction blocks that trace open patterns, such as a helical pattern, that can block radial paths of conduction without forming a closed ring within the vessel. However, such 3-D designs typically require a supporting wire to hold the 3-D shape, and a contracting mechanism or a dedicated lumen for the guide wire for straightening the catheter entering and advancing in the patient's body, all of which undesirably increases the outer diameter of the catheter. With an increased outer diameter, use of the catheter can be significantly limited.
Accordingly, there is a desire for a catheter having a collapsible 3-D shape that can be used with a guide wire without an increase in the outer diameter of the catheter, or at least in the portion of the catheter having the 3-D shape.